1. Field of the Invention
This invention relates to a radiation image read-out apparatus for use in a radiation image recording and reproducing system. This invention particularly relates to a radiation image read-out apparatus which is made small by efficient utilization of the space in the apparatus.
2. Description of the Prior Art
When certain kinds of phosphors are exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, they store a part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted by the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in U.S. Pat. Nos. 4,258,264, 4,276,473, 4,315,318 and 4,387,428 and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use a stimulable phosphor in a radiation image recording and reproducing system. Specifically, a sheet provided with a layer of the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet) is first exposed to a radiation passing through an object such as the human body to have a radiation image of the object stored thereon, and is then scanned with stimulating rays such as a laser beam which cause it to emit light in proportion to the stored radiation energy. The light emitted by the stimulable phosphor sheet upon stimulation thereof is photoelectrically detected and converted to an electric image signal, and the radiation image of the object is reproduced as a visible image by use of the image signal on a recording material such as a photographic film, a display device such as a cathode ray tube (CRT), or the like.
In the aforesaid radiation image recording and reproducing system, the stimulable phosphor sheet is used to temporarily store a radiation image until the sheet is scanned with stimulating rays to read out the radiation image. Therefore, after the radiation image is read out from the stimulable phosphor sheet, radiation energy remaining thereon should be erased to reuse the sheet.
For satisfying this requirement, it has been proposed to provide a radiation image read-out apparatus with a read-out section for reading out an image stored on a stimulable phosphor sheet, and an erasing section for erasing radiation energy remaining on the sheet.
As such read-out apparatuses, there has been proposed an apparatus provided with the image read-out section, the erasing section, and a cassette holding section for releasably holding a cassette which houses therein a single stimulable phosphor sheet carrying a radiation image stored thereon in the form housed in the cassette by use of an external image recording apparatus. In the proposed apparatus, the stimulable phosphor sheet is taken out of the cassette, sent to the image read-out section and the erasing section for carrying out image read-out and erasing on the stimulable phosphor sheet, and then conveyed into the empty cassette at the cassette holding section. In the case where the stimulable phosphor sheet on which the image read-out and erasing have been finished is returned in this manner into the cassette in the read-out apparatus, a loader or the like for loading the cassette with the stimulable phosphor sheet outside of the read-out apparatus prior to the next image recording step becomes unnecessary.
On the other hand, in an external image recording apparatus, besides the image recording on the stimulable phosphor sheet housed in the cassette, image recording may be carried out on a plurality of the stimulable phosphor sheets taken one by one out of a sheet feed magazine for continuous image recording or the like. The stimulable phosphor sheets each carrying a radiation image stored thereon are sequentially housed in a sheet housing magazine, which is then sent to a read-out apparatus for carrying out the image readout from the housed stimulable phosphor sheets. Therefore, the aforesaid read-out apparatus is often provided with the aforesaid cassette holding section and a magazine holding section for releasably holding the stimulable phosphor sheet magazine (i.e. the aforesaid sheet housing magazine). The stimulable phosphor sheets at the magazine holding section are taken one by one out of the stimulable phosphor sheet magazine, conveyed in the apparatus to the image read-out section and the erasing section for carrying out the image read-out and erasing on the stimulable phosphor sheets, and then sequentially conveyed into a tray held in the apparatus. The erased reusable stimulable phosphor sheets are then taken out of the apparatus in the form housed in the tray. Accordingly, the apparatus for carrying out the image read-out for both the stimulable phosphor sheet taken out of the cassette and the stimulable phosphor sheets taken out of the magazine must be provided with the cassette holding section, the magazine holding section and the tray holding section besides the image read-out section and the erasing section.
In recent years, it is required to make small the aforesaid radiation image recording and reproducing system as whole, and to make the aforesaid radiation image read-out apparatus as compact as possible for this purpose. However, with the conventional read-out apparatus, the apparatus cannot be made so small because of the provision of the conveyance path in the vicinity of the erasing section and the conveyance path from the erasing section to the cassette holding section and the tray holding section.
Specifically, in order to erase the radiation energy remaining on the stimulable phosphor sheet after the image read-out has been carried out thereon, it is necessary to expose the overall surface of the stimulable phosphor sheet to erasing light. Therefore, it is usually necessary for the erasing section to have a size not smaller than the size of a single stimulable phosphor sheet. In the case where the size of the erasing zone is smaller than the size of a single stimulable phosphor sheet, in order to carry out the erasing by moving the stimulable phosphor sheet so that the overall surface of the stimulable phosphor sheet is ultimately exposed to the erasing light, it is necessary to provide a guide means for supporting the stimulable phosphor sheet in the course of the erasing on the front and rear sides of the erasing section in the vicinity of the erasing zone. Therefore, in any case, the size of the erasing section or the size of the combination of the erasing zone with the guide means cannot always be made smaller than the length of a single stimulable phosphor sheet as viewed in the direction of conveyance of the stimulable phosphor sheet. Also, it is necessary for the stimulable phosphor sheet passing through the erasing section to be distributed and conveyed to the cassette holding section or to the tray holding section. Therefore, two conveyance paths are necessary after the passage of the stimulable phosphor sheet through the erasing section, and the apparatus becomes complicated and large.